1. Field of the Invention
The present invention relates to a hard disk drive, and more particularly to a technique for regulating current supplied for the unlatch operation when unlatching a head of a hard disk drive.
2. Description of the Related Art
In general, a hard disk drive(hereinbelow, referred to as HDD) widely used as an auxiliary memory device in a computer system is largely divided into two parts. A first part is a circuit part assembly(generally, called PCBA; Printed Circuit Board Assembly)on which most circuit components are mounted and a second part is a mechanism part assembly(generally, called HDA; Head Disk Assembly) which is equipped with most mechanism components including a head and a magnetic disk as well as a part of the circuit components.
In a hard disk drive assembly, a disk is rotatably mounted on a spindle motor and information is accessed by means of a read/write head mounted on an actuator arm which is rotated by a voice coil motor. Also, data transmitted from a host computer is recorded in the form of magnetic data on the disk by means of the same head. When the disk rotates at a constant speed, the head floats to a uniform height over the surface of the disk to record or reproduce data. The head is fixed at one side of the front end of the actuator and an iron piece is fixed to the other side thereof. The actuator is also supported by a pivot bearing and moves over the disk radially around the shaft of the pivot bearing under the control of the voice coil motor. A coil of the voice coil motor is mounted between the pivot bearing and the iron piece in the actuator. On both sides of the actuator, outer and inner crash stoppers are installed. The outer crash stopper is installed on a base so that the head can be prevented from deviating from the tracks on the disk and the inner crash stopper or a magnet comes into contact with the iron piece fixed to the other end of the actuator due to the magnetic force therebetween when the hard disk drive is not used so that the actuator can be fixed. These crash stoppers determine the movement range of the actuator, that is, the head stroke. The head stroke is the movement distance between the outermost circumferential region and the innermost circumferential region where the head is movable by the actuator over the disk.
In a multi-platter system, two or more disks are provided with a head for each respective surface of each disk.
The hard disk drive allows a head to be selectively positioned over any one desired track of the tracks on the disk by means of a servo mechanism. The positioning of the head over the specific track is normally performed by two servo control mode operations including a track seek operation and a track following operation. The track seek operation, which is generally called a seek mode, is the operation for moving a head from the present track to the desired track while the following operation, which is generally called a following mode, is the operation for enabling a head to accurately follow the sought track.
For the track seek and track following operations as well as the read and write operations of data, each track on the surface of a disk has a sector format including a data sector and a servo sector alternately disposed on a track corresponding to each head. The servo sector is prepared for the servo control of the track seek and following operations and the data sector is prepared for the writing of user data.
If the operation mode of the hard disk drive is switched from a latched non-operation state into an operating state, a microcontroller controls the head parked in a parking zone in such a manner that the head moves toward a data zone on the disk.
If the hard disk drive is in the operation state, the microcontroller controls the spindle motors so that it could be rotated at a constant speed and when the motor is rotated at a constant speed, the microcontroller enables the actuator to be moved from the parking zone toward the data zone with the actuator overcoming the latch force (magnetic force) of the magnet by supplying a square wave current of a uniform size to the actuator. The moving of the head from the parking zone to the data zone is called the unlatching operation. In such an unlatching operation, only a predetermined square wave of a uniform size is supplied at the acceleration and deceleration edges of the square wave.
After applying an unlatching current in the forward and reverse directions, the speed of the head is checked. In such an unlatching operation, the application of the unlatching current is accomplished with an open loop.
In such an unlatching operation, there has been a problem in that after the head is unlatched, the speed of the head may be greater or less than a desired value, thereby causing the unlatching operation to be unstable. The main cause of the variation of the speed of the head is that the latch force of the magnet may not be identical for each hard disk drive and may vary to a certain extent due to time or environmental factors even for one hard disk drive.
The following patents each disclose features in common with the present invention but do not teach or suggest the specifically recited technique for regulating the current supply for non-latch operation when unlatching a head of a hard disk drive: U.S. Pat. No. 5,305,160 to Funches et al., entitled Compensating For Variations In Torque Capability Of Voice Coil Motors, U.S. Pat. No. 5,305,161 to Giovanetti et al., entitled Adaptive Track Seeking For Disk Drives, U.S. Pat. No. 5,392,174 to Suzuki, entitled Method And Apparatus For Controlling The Speed Of Movement Of The Head Of A Disk Drive Apparatus To A Target Track, U.S. Pat. No. 5,675,558 to Katoh, entitled Seeking Control Apparatus And Method For Disk Drives, Using Slew-Rate Limit For Control Output, U.S. Pat. No. 5,521,891 to Nakane, entitled Speed Detection Apparatus, Speed Control Motor, And Track Jump Control Circuit, U.S. Pat. No. 5,465,034 to Andrews Jr. et al., entitled Low Acoustic Noise Seeking Method And Apparatus, U.S. Pat. No. 5,291,110 to Andrews Jr. et al., entitled Low Acoustic Noise Seeking Method And Apparatus, U.S. Pat. No. 5,600,219 to Gomez, entitled Sensorless Closed-Loop Actuator Unlatch, U.S. Pat. No. 5,384,675 to Crawforth et al., entitled Disk Drive With Controlled Actuator Oscillation For Release Of Head Carriers, U.S. Pat. No. 5,341,259 to Amirkiai et al., entitled Pivoting, Dual State Magnetic Latch For Disk File Actuator, and U.S. Pat. No. 5,568,333 to Bang, entitled Actuator Latching Device Of Hard Disk Drive.